Low-valent Alkaline Earth Metal Complexes: Synthesis, Structure and Reactivity

第一个锌(I)络合物Cp*锌锌Cp*的偶然发现激发了低价S块金属化学的研究活动。这导致了2007年发现了第一批以(Bdi)镁镁(Bdi)形式存在的镁(I)络合物，这类化合物受到了极大的关注，在化学上被发现是一种多功能的还原剂(bdi=-diketiminate配体)。除了稀有的Be(0)或Be(I)物种和一个Ca(I)络合物外，迄今还没有较重的碱土(Ae)金属Ca、Sr和Ba的(BDI)AeAe(BDI)络合物的例子。我们试图分离一个(BDI)CaCA(BDI)配合物，结果导致芳香族溶剂或N_2的2e-还原，形成(BDI)Ca(芳烃)Ca(BDI)或(BDI)Ca(N_2)Ca(BDI)配合物。与Frenking(Marburg)合作的理论分析表明，Ca上的d-轨道在氮气活化中起着重要作用。分离钙-氮络合物的关键是一种超大的-二酮基配体，由于3-戊基取代基，它能够使用烷烃溶剂。一个更大的BDI配体被用来裂解(BDI)镁镁(BDI)中的镁-镁键，这将导致一个高活性的，迄今未知的(BDI)镁自由基。这一尝试导致了一个独特的(Bdi)镁ˉNa+络合物的分离，其中零价镁中心带有-1的形式电荷。该项目的目标是：1)使用光谱方法(核磁共振、电子顺磁共振和钙价对核X射线发射光谱研究)和理论(部分合作)加深我们对(BDI)Ca(芳烃)Ca(BDI)和(BDI)Ca(N2)Ca(BDI)络合物成键的认识。我们的主要兴趣是d轨道在成键中的重要性2)通过设计更大的配体(L)将这一化学扩展到较重的Ae金属Sr和Ba，并试图分离我们研究的原始目标LaEAeL。3)研究了LaE(芳烃)AEL、LaE(N2)AEL和LAeAeL络合物的芳烃和氮气官能化及其极端氧化还原活性。4)利用超大分子配体分离LMG自由基。5)研究新化合物类(Bdi)MgˉNa+与亲核镁中心的反应性，这是目前的无人区。6)开发了重Ae金属Ca、Sr和Ba的LaE-ˉ-M+络合物的一般路线。7)使用(Bdi)MgˉNa+试剂，通过与MXN(X=卤化物，M=S-，p-或d-嵌段金属)的盐歧化反应生成金属镁键。8)用DFT、NBO和AIM方法对新的复合体进行理论分析。我们的目标是与两名博士生一起运行该项目，并预测输出8-10篇完整的论文，这些论文可能会发表在高影响力的期刊上。

The serendipitous discovery of the first Zn(I) complex, Cp*ZnZnCp*, has stimulated research activities in low-valent s-block metals chemistry. This led in 2007 to discovery of the first Mg(I) complexes in the form of (BDI)MgMg(BDI), a compound class that received enormous attention and was found to be a versatile reducing agent in chemistry (BDI = -diketiminate ligand). Apart from rare Be(0) or Be(I) species and a Ca(I) complex, there are hitherto no examples for (BDI)AeAe(BDI) complexes of the heavier alkaline earth (Ae) metals Ca, Sr and Ba. Our attempts to isolate a (BDI)CaCa(BDI) complex resulted in 2e-reduction of either the aromatic solvent or N2 and formation of (BDI)Ca(arene)Ca(BDI) or (BDI)Ca(N2)Ca(BDI) complexes. Theoretical analyses in cooperation with Frenking (Marburg) showed that d-orbitals on Ca play an essential role in N2 activation. The key to isolation of the Ca-N2 complex is a superbulky -diketiminate ligand that, due to 3-pentyl substituents, enables use of alkane solvents. An even bulkier BDI ligand was used in an effort to cleave the Mg-Mg bond in (BDI)MgMg(BDI) which would result in a highly reactive, hitherto unknown, (BDI)Mg● radical. This attempt led to isolation of a unique (BDI)MgˉNa+ complex in which the zerovalent Mg center carries a formal charge of -1. This new class of magnesyl sodium complexes features an electron-rich Mg center and displays reactivity that is a complete opposite of that of common Mg complexes with positively charged Mg2+ centers.Project aims:1) Deepening our knowledge on bonding in an extended series of (BDI)Ca(arene)Ca(BDI) and (BDI)Ca(N2)Ca(BDI) complexes using spectroscopic methods (NMR, EPR and Calcium Valence-to-Core X‑ray Emission Spectroscopy studies) and theory (partially in collaboration). Our main interest is the importance of d-orbitals in bonding.2) Extending this chemistry to the heavier Ae metals Sr and Ba by design of bulkier ligands (L) and attempts to isolate LAeAeL, the original target of our studies. 3) Studying arene or N2 functionalization and the extreme redox-reactivity of LAe(arene)AeL, LAe(N2)AeL and LAeAeL complexes.4) Isolation of LMg● radicals using superbulky ligands. 5) Investigating the reactivity of the new compound class (BDI)MgˉNa+ with nucleophilic Mg centers that is currently a no-man’s land. 6) Developing a general route to LAeˉM+ complexes for the heavier Ae metals Ca, Sr and Ba. 7) Use the (BDI)MgˉNa+ reagent to create Mg-metal bonds following a salt metathesis route with MXn (X = halide, M = s-, p- or d-block metal). 8) Theoretical analysis of new complexes with DFT, NBO and AIM methods.We aim to run the project with two PhD students and forecast an output of 8-10 full papers which will likely be published in high-impact journals.